Terminals are typically crimped onto wires by means of a conventional crimping press having an anvil for supporting the electrical terminal and a die that is movable toward and away from the anvil for effecting the crimp. In operation, a terminal is placed on the anvil, an end of a wire is inserted into the ferrule or barrel of the terminal, and the die is caused to move toward the anvil to the limit of the stroke of the press, thereby crimping the terminal onto the wire. The die is then retracted to its starting point.
In order to obtain a satisfactory crimped connection, the crimp height and other characteristics of the crimped terminal must be closely controlled. The crimp height of a terminal is a measure of height or maximum vertical dimension of a given portion of the terminal after crimping. Ordinarily, if a terminal is not crimped to the correct crimp height for the particular terminal and wire combination, an unsatisfactory crimped connection will result.
A simple non-destructive means of determining crimp height during the crimping process is disclosed in U.S. Pat. No. 4,856,186 which issued Aug. 15, 1989 to Yeomans and U.S. Pat. No. 4,916,810 which issued Apr. 17, 1990 to Yeomans, both of which are incorporated by reference as though set forth verbatim herein. The '186 patent sets forth a procedure for determining the crimp height by monitoring the ram position and the force imposed on the terminal during the crimping operation. As the crimping dies engage the terminal and crimping begins, the crimp force builds up to a peak and then begins to recede. At the exact instant that the receding force reaches zero, the position of the ram is noted and the distance between the two mating halves of the crimping die set is calculated. This is then translated into the crimp height of the crimped connection. Such a procedure assumes that at the instant the force equals zero that the mating halves of the die set are just beginning to disengage the crimped terminal. FIG. 3 shows a work curve graph which illustrates this. There, the graph 5 depicts the relationship of the crimp force on the terminal with respect to displacement of the ram. As the crimping die set engages the terminal to begin the crimp, the force begins to increase as shown at E1. The force reaches a peak at E2 and then falls off as the crimping die set halves begin to separate. As this force fall-off continues, the normal expectation would be that the point E3 would be the point where the force recedes to zero, however, this is not the case. As can be seen in the graph 5, as the force recedes close to zero the force fall-off becomes slowed somewhat causing a sharp turn in the graph 5 and does not actually reach zero until the point E4 is reached. If the crimp height is calculated based upon the point E4, an erroneous crimp height will result.
What is needed is a procedure for avoiding such a result and, at the same time, utilizing the information yielded by the graph 5 between the points E2 and E3 to more accurately determine the crimp height. Such a procedure could then be utilized in automated terminating machines to provide reliable feedback of machine performance so that corrective adjustments may be made prior to adversely affecting production. Such feedback and corrective adjustments in automated crimping machines are disclosed in the above-mentioned '810 patent as well as U.S. Pat. Application Ser. No. 07/529,036 filed May 25, 1990 by the assignee of the present application and which is incorporated by reference as though set forth verbatim herein.